std::conditional_t Type Selection

Implement Storage<T> whose value_type is T for small types (<= 8 bytes) but std::shared_ptr<T> for large ones — via std::conditional_t — plus biggest(a, b) returning the larger by reference using std::conditional_t on a comparison trait is overkill; just use std::conditional_t<std::is_integral_v<T>, int, double> fallback semantics in numberKind<T>().